$N_{boards} = \lceil \frac{DeckLength_{total\_inches}}{BoardWidth_{inches} + BoardGap_{inches}} \rceil$
$L_{decking} = N_{boards} \times DeckWidth_{feet} \times (1 + \frac{Wastage \%}{100})$
$N_{joists} = \lceil \frac{DeckLength_{total\_inches}}{JoistSpacing_{inches}} \rceil + 1$
$L_{joists} = N_{joists} \times DeckWidth_{feet}$
$N_{screws} = N_{boards} \times N_{joists} \times 2$